What is violet at the end of the visible spectrum, then? We call the higher wavelength stuff ultraviolet, and violet looks purple to me, so I’m having trouble reconciling this stuff with what you’re saying.
We call it that but our eyes see the far end frequency as a colour that only very slightly activates blue sensitive cone receptors and no others. For red sensitive cones there is a slight bump in the high end frequencies also that makes it possible for them to look violet as it activates the blue sensitive and a bit of red sensitive receptors but a much purpler purple is made by combining high and low frequencies.
There is evidence to show that violet does actually weakly activates red cones too. This is because the violet light starts creeping up to double the frequency of the lower end of the red sensitivity, and so it can actually successfully activate it very weakly. There are other factors that can lessen or even fully negate that effect though, it’s all kind of fuzzy.
What is violet at the end of the visible spectrum, then? We call the higher wavelength stuff ultraviolet, and violet looks purple to me, so I’m having trouble reconciling this stuff with what you’re saying.
Violet and purple are distinct terms here.
We call it that but our eyes see the far end frequency as a colour that only very slightly activates blue sensitive cone receptors and no others. For red sensitive cones there is a slight bump in the high end frequencies also that makes it possible for them to look violet as it activates the blue sensitive and a bit of red sensitive receptors but a much purpler purple is made by combining high and low frequencies.
https://www.researchgate.net/figure/Normalized-spectral-sensitivity-of-retinal-rod-and-cone-cells_fig7_265155524
There is evidence to show that violet does actually weakly activates red cones too. This is because the violet light starts creeping up to double the frequency of the lower end of the red sensitivity, and so it can actually successfully activate it very weakly. There are other factors that can lessen or even fully negate that effect though, it’s all kind of fuzzy.